Urea Delivery Tank Module

ABSTRACT

A liquid reductant dosing module for a combustion exhaust treatment system is disclosed comprising:
         (a) an enclosed reservoir comprising a top, a bottom, one or more sides, an inlet, and an outlet;   (b) a heater disposed in the reservoir;   (c) a filter element disposed between the outlet and the liquid reductant in the reservoir; and   (d) a heat sink member in thermal contact with the heater, disposed between the filter element and the outlet.

BACKGROUND OF THE INVENTION

This invention relates to a reservoir for a fluid dosing system. Morespecifically, the invention relates to a reservoir for holding areducing agent for introduction into a combustion exhaust gas.

The emission of nitrogen oxide (NO_(x)) compounds in engine exhausts haslong been the focus for health professionals and regulatory agenciesworldwide. In many locations, regulations require stringent reductionsof NO_(x) levels in new equipments. NO_(x) emissions may be found in avariety of systems such as internal combustion engines, gas turbineexhaust, lean burn engines, industrial boilers, process heaters or otherprocess streams.

In order to reduce NO_(x) emissions, it is known to use a selectivecatalytic reduction (SCR) device to treat an exhaust flow and tosignificantly reduce NO_(x) emissions. In an SCR system a reducingagent, for example urea solution, is dosed into the exhaust gas flowupstream of an SCR catalyst. This reducing agent is then usually reactedin the presence of a catalyst downstream of the injection point in anSCR device. Within the SCR device NO_(x) compounds are then reduced tonitrogen. WO2004111401 discloses such a device.

The general operation of an SCR device is shown in FIG. 1, in which adiesel engine 1 produces an exhaust flow comprising various exhaustgases 3. The exhaust gases are conveyed through an exhaust system,indicated generally at 5, comprising an oxidation catalyst device 7, aselective reduction catalyst device 9 and a slip catalyst 11.

The oxidation catalyst device 7 is a flow through device that consistsof a canister containing a honeycomb-like structure or substrate. Thesubstrate has a large surface area that is coated with an activecatalyst layer. This layer contains a small, well dispersed amount ofprecious metals such as platinum or palladium. As the exhaust gasestraverse the catalyst, carbon monoxide, gaseous hydrocarbons and liquidhydrocarbon particles (unburned fuel and oil) are oxidized, therebyreducing harmful emissions.

The SCR device 9 performs SCR treatment of NO_(x) using ammonia derivedfrom a source of urea as a chemical reductant. A slip catalyst 11 may belocated downstream of the SCR device 9 to clean up any unreactedammonia.

Urea for the SCR device 9 is stored in a tank 13 which is in fluidcommunication with the exhaust system 5. A pump 15 is provided to pumpurea from the tank 13 to the exhaust system 5. The supply of urea iscontrolled by a control unit 17, for example the engine control unit,which receives engine speed and other engine parameters from the engine1. An injection device 19 (also referred to herein as a fluid dosingdevice) is used to inject the urea into the exhaust flow.

As a 32.5% urea solution freezes at −11.5° C., urea delivery systemsmust be adapted for delivery of liquid urea to the vehicle exhaustsystem under conditions that would normally cause the liquid urea tofreeze. One solution would be to simply heat the storage tank 13.However, this can require substantial quantities of energy to maintainthe entire storage tank 13 in a liquid state and can take significanttime to thaw if the tank has become completely frozen. An alternativearrangement is to place a smaller reservoir downstream of the storagetank that can be unfrozen quickly and/or maintained as liquid moreefficiently since it contains a smaller amount of liquid urea. Such anarrangement is shown in FIG. 2, with urea flowing from storage tank 23into dosing reservoir 33 through inlet 25, and then pumped out of dosingreservoir 33 by pump 15 through outlet 27 from where it flows to theexhaust stream as shown in FIG. 1. Alternatively, the dosing reservoircan be positioned adjacent to and in physical contact with the storagetank or even inside the storage tank so that heat from the heated dosingreservoir during prolonged periods of operation will help thaw thestorage tank or maintain it in a liquid state.

In any case, a liquid reductant reservoir (whether it is storage tank 13or smaller dosing reservoir 33) will need to be heated in order toprovide liquid reductant to the exhaust system. One proposed approachhas been to use a submerged ceramic PTC heater in the reservoir.However, this approach provides heat at the bottom of the reservoir, butnot at the top. As liquid reductant is dosed into the exhaust system,the level in the reservoir drops, resulting in a cavity of dead airspace forming between the frozen reductant toward the top of thereservoir and a level of liquid underneath, which can result in poorheat transfer to the remaining frozen urea. Further, as the liquid urealevel continues to drop, the ceramic PTC heater element may itselfbecome exposed to air, at which point its self-regulating heatingfunction will result in restricted power to the heater for furthermelting of frozen urea.

An alternative heater approach is to use a vertical ceramic PTC rodheater that runs from the top to the bottom of the urea reservoir. Thisapproach can provide good heating near the top of the reservoir, but maynot heat the bottom quickly enough to provide liquid urea for exhausttreatment right after vehicle startup. Also, as the urea level dropsduring dosing, exposure of the top of the ceramic PTC rod heater to theair can result in power reduction due to the heater's self-regulatingfunction.

Therefore, there is a need in the art for providing heat to a reservoirfor use in a dosing system that addresses the above mentioned problems.

SUMMARY OF THE INVENTION

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

According to the present invention, there is provided a liquid reductantdosing module for a combustion exhaust treatment system comprising:

-   -   (a) an enclosed reservoir comprising a top, a bottom, one or        more sides, an inlet, and an outlet;    -   (b) a heater disposed in the reservoir;    -   (c) a filter element disposed between the outlet and the liquid        reductant in the reservoir; and    -   (d) a heat sink member in thermal contact with the heater,        disposed between the filter element and the outlet.

In one exemplary embodiment, the outlet, heater, filter element, andheat sink member are integrated together in a module that is mounted tothe bottom of the reservoir. More specifically, this bottom-mountedmodule may comprise:

-   -   (a) a holder element having a circumferentially-disposed        mounting flange for mounting to the bottom of the reservoir, at        least one vertical sidewall connected to the mounting flange,        and a recessed bottom connected to the at least one vertical        sidewall, the recessed bottom having an opening for the outlet        opening therein;    -   (b) a screen member disposed above and substantially parallel to        the recessed bottom; and    -   (c) a filter medium disposed below the screen member, thereby        forming an interstice between the filter medium and the outlet        opening in the recessed bottom;        wherein the heater extends through an opening in the screen and        the heat sink member is thermally connected to the heater and        extends into the interstice

Among other things, the invention provides a protected environment inthe space between the filter element and the reservoir outlet that isheated by the heat sink member so that it can be readily thawed ormaintained as liquid, from which liquid reductant may be readily drawnfollowing a cold startup under freezing conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 depicts a known SCR system.

FIG. 2 depicts a known reservoir configuration for dosing liquidreductant as part of an SCR system.

FIG. 3 shows an exemplary liquid reductant dosing module according tothe invention.

FIG. 4 shows an exemplary liquid reductant dosing module according tothe invention.

FIG. 5 depicts a perspective view integrated module of an outlet,heater, filter element, and heat sink member that us useful in anexemplary embodiment of the invention.

FIG. 6 shows a side view of the integrated module of FIG. 4 in anexemplary liquid reductant dosing module according to the invention.

DETAILED DESCRIPTION

Referring now to the Figures, the invention will be described withreference to specific embodiments, without limiting same. Turning now toFIGS. 3, and 4, there is shown a cross-section view of a liquidreductant reservoir 33 of the type shown in FIG. 2. Of course, theinvention is applicable to any sort of vessel for liquid reductant aswell, such as a reductant storage tank 13 as shown in FIG. 1. Rod heater32 is mounted through an opening in the top of the reservoir, andelectric leads 34 provide power to the heater. In an exemplarynon-limiting embodiment, the heater can be overmolded into the cover.The heater of any known sort that is suitable for submerged use inliquid reductants such as urea. In one exemplary embodiment, the heateris self-regulating such as a PTC (positive temperature coefficient)heater, which may use a metalized positive temperature coefficientceramic in the heating element whose resistance increases as a functionof increasing temperature. Such varying resistance makes the heaterself-regulating and avoids over-heating. Another exemplaryself-regulating rod heater useful as rod heater 32 is more fullydescribed in the U.S. patent application Ser. No. 12/638,364 filed onDec. 15, 2009 entitled “Liquid Reductant Dosing Module with HeatingDevice”, the disclosure of which is incorporated herein in its entirety.This heater has a hollow tube made out of a material such as stainlesssteel with windings along the inside of the tube of a resistive materialthat provides heat when electric current is run through it.Self-regulation of resistance heaters can also be accomplished throughcontrol circuitry (e.g., a Wheatstone bridge control circuit) or throughmicroprocessor control of the power supplied to the heater. Other typesof heaters and configurations, e.g., dome heaters, or PTC heaters havingrod or dome configurations, may also be used as is known in the art.

With further reference to FIGS. 3 and 4, the reservoir 33 also has aliquid reductant inlet (not shown) and an outlet in the form of pickuptube 31. Pickup tube 31, which may be of any suitable material, e.g.,stainless steel, is also affixed to top of reservoir 33 and extendsdownward through an opening in reservoir 33 to draw liquid reductantfrom near the bottom of the reservoir. In an exemplary embodiment, thepickup tube 31 is in contact with or is proximate to the rod heater 32in order to limit any frozen blockages in the pickup tube. In oneexemplary embodiment as shown in FIG. 3, the pickup tube 31 is inside ahollow rod heater 32. In another exemplary embodiment as shown in FIG.4, the pickup tube is adjacent to rod heater 32.

With continuing reference to FIGS. 3 and 4, there is shown a filterelement 36 is disposed around the open end of pickup tube 31 and one ormore heat sink members 35 are disposed in the space between the open endof pickup tube 31 and the filter element 36. The filter element 36 canbe of any configuration that is effective to filter liquid reductantbefore it enters the open end of pickup tube 31, but as shown in FIGS. 3and 4 is a pillow-shaped filter element. The filter element comprises afilter medium that can be any of a number of well-known filter mediadepending on the filtration requirements for the liquid reductant dosingsystem and its components, e.g., the pump. In one exemplary embodiment,the filter medium is a stainless steel mesh with a mesh size of 7 to 70μm. Other materials may be used instead of stainless steel, such asacetal or polyoxymethylene. In another exemplary embodiment, especiallywhere the filter medium is supported, the filter medium may be a highefficiency media having a mesh size of 7 to 70 μm, or may be acombination of multilayer media with varying mesh sizes.

Heat sink member 35, which may be of any suitable conductive materialthat is compatible with the liquid reductant environment (e.g., aluminumwith an anodized surface or PTFE coating, stainless steel, or any otherheat-conductive metal that is compatible with the liquid reductantenvironment), is connected to the bottom area of rod heater 32 toenhance transfer of heat from rod heater 32 to the liquid reductant inthe reservoir, and more particularly to maintain the area inside offilter element 36 in a liquid state.

Turning now to FIGS. 5 and 6, there is shown an alternate configurationof an exemplary embodiment of the invention having an integrated modulecomprising an outlet port, heater, filter element, and heat sink memberthat is suitable for mounting on the bottom of a liquid reductantreservoir. Reference characters for FIGS. 5 and 6 match those for FIGS.3 and 4 for analogous components, e.g., reservoir 33, heater 32, etc.FIG. 5 is a perspective view of the integrated module itself, and FIG. 6is a cross-section view of the integrated module mounted in a liquidreductant reservoir. Referring to both FIGS. 5 and 6, holder 37 havingmounting flange 38 is mounted in an opening in the bottom of liquidreductant reservoir 33 by known techniques such as welding or with athreaded fitting. A central opening in the bottom of holder 38accommodates electric leads 34 for centrally-mounted heater 32. Anothercentral opening in the bottom of holder 37 accommodates outlet 31, whichis in fluid communication with liquid reductant in the reservoir 33.Protective screen 39 is disposed along the top surface of the holder 37radially inward from the mounting flange 38, and filter media 36 isdisposed thereunder. Optionally, a second screen may be used underneaththe filter media 36 so that the filter media is sandwiched between twoscreens, thus providing support and structural integrity. Screen 39screens out any large particles in the liquid reductant as well asprotecting the filter media 36 against damage from penetration by icecrystals that may form in the main body of the reservoir 33. Holder 37,flange 38, and screen 39 may made of any suitable material such asstainless steel, nylon materials such as Zytel®, or polyphthalomidessuch as Amodel®. Heat sink member 35 is disposed in the intersticebetween the filter media 36 and the outlet 37, and helps thaw and/ormaintain the liquid in that space in liquid form, providing amini-reservoir of reductant in liquid form available for dosing into anexhaust system immediately or shortly after a cold startup underfreezing conditions.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description.

1. A liquid reductant dosing module for a combustion exhaust treatment system comprising: (a) an enclosed reservoir comprising a top, a bottom, one or more sides, an inlet, and an outlet; (b) a heater disposed in said reservoir; (c) a filter element disposed between said outlet and the liquid reductant in said reservoir; and (d) a heat sink member in thermal contact with said heater, disposed between said filter element and said outlet.
 2. A liquid reductant dosing module according to claim 1 wherein said outlet is located proximate to the bottom of said reservoir.
 3. A liquid reductant dosing module according to claim 1 wherein said outlet comprises a pickup tube extending along a first axis extending between the bottom of said reservoir and the top of said reservoir, said pickup tube having an open end proximate to the bottom of said reservoir.
 4. A liquid reductant dosing module according to 3 wherein said heater is a rod-shaped heater extending along a second axis, which may be the same as or different than said first axis, extending between the bottom of said reservoir and the top of said reservoir.
 5. A liquid reductant dosing module according to claim 4 wherein said rod-shaped heater is hollow and wherein said pickup tube is disposed inside said rod-shaped heater.
 6. A liquid reductant dosing module according to claim 5 wherein said pickup tube is disposed adjacent to said rod-shaped heater.
 7. A liquid reductant dosing module according to claim 6 wherein said heat sink member is in thermal contact with said pickup tube.
 8. A liquid reductant dosing module according to claim 1 wherein said heater is a rod-shaped heater extending along a second axis extending between the bottom of said reservoir and the top of said reservoir.
 9. A liquid reductant dosing module according to claim 1 wherein said heat sink element comprises aluminum having an anodized aluminum layer or a polytetrafluoroethylene coating thereon or stainless steel.
 10. A liquid reductant dosing module according to claim 1 wherein said filter element comprises a stainless steel mesh, acetal, or polyoxymethylene filter media.
 11. A liquid reductant dosing module according to claim 1 wherein said outlet, heater, filter element, and heat sink member are integrated together in a module that is mounted to the bottom of said reservoir.
 12. A liquid reductant dosing module according to claim 11 wherein said bottom-mounted module comprises: (a) a holder element having a circumferentially-disposed mounting flange for mounting to the bottom of said reservoir, at least one vertical sidewall connected to said mounting flange, and a recessed bottom connected to said at least one vertical sidewall, said recessed bottom having an opening for said outlet opening therein; (b) a screen member disposed above and substantially parallel to said recessed bottom; and (c) a filter medium disposed below said screen member, thereby forming an interstice between said filter medium and the outlet opening in said recessed bottom; wherein said heater extends through an opening in said screen and said heat sink member is thermally connected to said heater and extends into said interstice. 